Process for the reduction of the free acidity in mineral lubricating oils



ilnited rates This invention relates to a method of reducing the content of acidic oxygenated compounds in hydrocarbon mixtures containing same, and, more particularly, to a process for the reduction of the acid neutralization number of mineral lubricating oils. More specifically, the invention relates to the discovery that heavy petroleum oils, such as solvent extracts obtained as by-products from the solvent refining of mineral lubricating oils, which solvent extracts may contain relatively high contents of naphthenic acids and related acidic materials, when heated with urea at a temperature of above about 400 F. and up to about 550 F., undergo a substantial reduction in acid neutralization number.

It is known that acidic oxygenated materials such as naphthenic acids can be neutralized and more or less extracted from various petroleum stocks, such as lubricating stocks, by treatment with various neutralizing agents and solvents. However, it is diflicult, by these known processes to obtain products of reduced acid neutralization number which do not contain appreciable quantities of naphthenate salts. Such naphthenate salts in lubricants can be very troublesome during use of the lubricant. Sodium naphthenates tend to increase emulsification of the oil with water while ammonium naphthenates may, during use of the lubricant, cause deterioration of bearings, such as those of copper and lead. Ammonium naphthenates also tend to promote emulsification of the lubricant with water.

In accordance with the present invention, we have found that urea, used either in stoichiometric amounts or in excess of stoichiometric amounts, reacts with the naphthenic acids and other acidic materials in mineral lubricating oils to form stable amides which do not revert to any free acids during use or storage of the treated oil. is insoluble in the oil, it settles out rapidly, and the treated oil can be decanted from the excess urea and used Without further treatment. The naphthenic acids and other oxygenated materials are not removed from pctroleum oils by the process of this invention, but are converted to substances having no free acidity, termed amides for the purposes of this invention. In addition, as part of the invention, we have found that the tem perature is essentially critical; the reaction is slow at 400 F., and becomes rapid in the neighborhood of about 450 F., but at temperatures above 550 F. the decomposition of urea becomes rapid and competes with the amideforming reaction.

Another feature of this invention is the discovery that by incorporating urea in mineral lubricating oils during their distillation, the products and the residue have low acid neutralization numbers.

Still another feature of the invention is the discovery that the unusual reduction in the acid neutralization number can be accomplished by contacting the oil with an adsorbent in the presence of urea at temperatures between about 400 F. and 550 F.

Accordingly, it becomes a primary object of this invention to provide a process for reducing the acid neutralization number of mineral lubricating oils.

Another object of this invention is to provide a process for reducing the acid neutralization number of mineral lubricating oils by treatment of the oil with urea.

Also, since any excess urea used in the reaction atent C ice Another object of this invention is to provide a process for reducing the acid neutralization number of mineral lubricating oils by treatment with urea at temperatures ranging from about 400 F. to 550 F.

Another object of this invention is to provide a process for reducing the acid neutralization number of solvent extracts by treatment with urea at temperatures ranging from 400 F. to 550 F.

In order to demonstrate the invention, examples are given:

EXAMPLE 1 A three-necked, 500-cc. glass flask was equipped with a mechanical stirrer, thermometer, and nitrogen-delivery tube. Into the flask was placed 300 cc. of extract oil (sample 5, Table I) from the production of 170 viscosity neutral. This extract oil had an acid neutralization number of 6.5, due to its content of naphthenic acids. A Glas-Col heating mantle was placed around the flask, and the oil in the flask was stirred mechanically under a blanket of nitrogen while the temperature was raised to 450 F. During a period of 4.2 hours, a total of 4 grams of urea was sifted into the hot oil at 15- minute intervals. At the end of this period, the acid the following neutralization number of the oil had dropped to 3.7. The

excess of urea was insoluble in the oil and settled to the bottom of the flask after the stirring was discontinued.

EXAMPLE 2 A -cc. sample of the same extract oil as used in Example 1 was heated with 5 grams of urea at 450 F. without stirring, but under a blanket of nitrogen. At the end of 4 hours, the neutralization number of the oil was 5.2. A comparison of this result with that of Example 1 showed that the rapidity of reduction in acid neutralization number of the oil was closely dependent on intimate contact of the oil with the oil-insoluble urea.

EXAMPLE 3 A 300-cc. sample of the same extract oil as used in Example 1 was heated with urea under the same conditions except that the temperature was 400 F. instead of 450 F. At the end of 3 hours, the acid neutralization number of the oil was 6.3. A comparison of this result with that of Example 1 showed that the rate of reaction of urea with the naphthenic acids in the oil was very slow at 400 F but was appreciable at 450 F.

The foregoing examples illustrate that the treatment with urea is successful in reducing the acid neutralization number toa low value. This reduction in acid neutralization number is considered to be unusually great because of the high acid number of the solvent extracts treated, and the peculiar nature of the naphthenic acids present in solvent extracts which the art recognizes as making them exceedingly diflicult to remove or neutralize.

The following example is given to illustrate the distillation of an oil in the presence of urea.

EXAMPLE 4 A 400-cc. sample of aromatic extract oil (sample 5, Table I) from the production of viscosity neutral oil, having an acid neutralization number of 6.5, is distilled under vacuum with four times the quantity of urea stoichiometrically required for the naphthenic acids present. The temperature is maintained above 450 durexamples are given.

EXAMPLE A three-necked; 500m?- glass flask was equipped With a .5 treatment which lowers the acid neutralization number mechanical stirrer, nitrogen-delivery tube. and thefmomis included as a material susceptible to treatment. Lutitfli into the hash s Placed 300 f bricating oil fractions, particularly neutral oils, bright bright Stock p Table which an acld stocks, and solvent extracts from the manufacture of neutr lizati n m r f 01 A (has-C01 heating neutral oils and bright stocks, can be advantageously mantle was Placed around the hash, and Oil in the treated in accordance with the instant process. The term flask Was Stirred mechanically under a blanket of nitrogen solvent'extract as used herein is intended to mean the While the temperature Was Taised' 4 Then a extract product resulting from the treatment of lubricatmiXtur f urea and Fi t 60 y, Corresponding to ing oils and lubricating oil fractions with a selective solof llffia and 5 of }3 p barrel of the on being vent for the purpose of separating, in the extract phase, treated, was added to the 011 in the fiask- Thfi mixture those materials which are predominantly aromatic in was maintained at 450 F. for 30 minutes under a blanket nature f om 1 edominantly naphthenic and paraffinic of nitrogen, with constant mechanical agitation. Then materials which appealin the ffi t phasa Solvent th h at g mantle i removed and the agltatioh extracts are produced as by-products from the solvent tlnllfid u l 011 III the hash d cooled to refining processes presently applied in the manufacture of. T Oil InlXthrB was then filtered y Suction through modern lubricating oils. Various solvents are used for C'elite filter The filtered had a good OdOI' and an this pur gse including phenol furfural nit obenzene, a nehtfahlatloh number of y mixtures of sulfur dioxide and nitrobenzene, mixtures EXAMPLE phimol andlwater, and the well-known lguosol solventi. 1s atter so vent comprises a mixture 0 ro ane an Anothflr Porno of the unfifnshtd bnght Stock was cresylic acid. Since solvent extraction and th solvent treated n the same manner as in Example 5 except t extracts produced thereby are well known, there is no the urea Y (.Hmtted The filtered obtained had necessity for further description for purposes of this in markedly inferior odor, as compared to the filtered Oll vention It suflices to Sa that one killed th t from Example 5, and an acid neutralization number of y S i e at 0-10- may have reference to one or more of the United States Although the process of this invention is designed to paterits Whlch de'scnbe.m greater detalhflie solvent exdestroy the free acidity of acidic oxygenated materials in traction process and give the characteristics of solvent hydrocarbon mixtures containing same, it is particularly fzxtracis that may be benefited the Process of thls applicable to the destruction of the free acidity of naphmvemlonthenic acids in lubricating oils and fractions, including The touowlhg table Elves the P i/ and chel'hlcal solvent extracts from the manufacture of both neutral oils and bright stocks. The naphthenic acids found in lubricating oil and fractions thereof are generally characterized as high-molecular-weight carboxylic acids,

Various types of hydrocarbon oil mixtures containing acidic oxygenated materials, including naphthenic acids, may be treated in accordance with this invention. Any hydrocarbon oil fraction which can he improved by a properties of several solvent extracts and lubricating oil fractions which are illustrative of the types of material that may be treated in accordance with this invention.

Table I.-Characteristics of Oils and Extracts That May Be Benefited by the Process of This Invention A. LUBRICATING OIL EXTRACTS Saybolt Viscosity Acid Sample API Flash Fire (see) at- Neutral- Pour Name No. Gravity F.) F.) izgion F.)

Extract 1 l8. 0 110 0. 6 105 Residual Extract. 2 8. 9 569 0. 7 75 D0 3 8. 8 505 4. 0 85 Short Besid. Extract- 4 14. 5 268 2. 5 70 Aromatic Extract Oil-.- 5 11.7 62 6. 5 Extract 5 7. 9 73 3. 2 25 Heavy Extract 7 13. 1 370 2. 5 Aromatic Extract RP 8 9.1 796 4. 8

B. SOLVENT BEFINED OILS Neutral 9760 9 22. 4 435 500 355 51 0. 17 0 Medium Neutral Stock. 10 31. 2 420 485 172 45 0. 0G 0 N0. 200 Neutral Stock 11 29.0 430 490 205 46 0.06 -5 Viscous Neutral 12 29. 6 500 565 516 65 O. 06 0 Bright Stock M-4010 13 24. 6 595 655 3, 191 170 0.31 5 Unfinished Bright Stock 14 26. 7 580 640 2, 454 154 0.18 0

O. NON SOLVENT REFINED OILS Cyiinder Stock AG 15 21.0 555 625 214 0. 07 15 Black Oil 16 19.0 655 60 0. 6

liquid and/or solid in physical state, containing mostly alicyclic or condensed alicyclic nuclei. These naphthenic acids show little or no unsaturation and consist essentially of acids boiling above about 600 F. Naphthenic acids falling Within the foregoing definition are considered in the art to oifer the greatest difl-iculties in re-.

moval from the hydrocarbon source.

The process of this invention may be carried out by any of the known methods of treating hydrocarbon mixtures with a solid or liquid treating agent provided the temperature of such treatment is maintained in the range of above about 400 F. to about 550 F. The process may be carried out batchwise or continuously using any of the various contacting apparatus available for this type of reaction.

Since the desired amide formation is always accompanied by some decomposition of the urea, it is preferable to use more than one to one molar ratio of urea to naphthenic acid. In practice, an amount of urea is used which is from one and one half to four times the quantity theoretically required to convert the naphthenic acids to amides. Any amount of urea may be used in practice, the upper limit being dictated by economic considerations.

The urea may be added to the oil in any convenient fashion, either before, during, or after the oil has been raised to the required temperature. It may be added in increments at definite time intervals, if desired. Since urea is a solid at ordinary temperatures and has a relatively low melting point, it may be sifted into the hot oil or it may be added as a liquid. In continuous operation the urea may be mechanically proportionated into the oil stream either in solid or liquid form.

For the best operation of this process, the oil is blanketed with an inert gas such as nitrogen, methane or natural gas to prevent atmospheric oxidation of the oil. Some provision must also be made for the gases liberated in the process. Ammonia is liberated during the reaction of amide formation and also from any concurrent decomposition of urea. In case water is present, carbon dioxide may also be liberated.

The time required for reaction of the urea with the oil at the process temperature is dependent upon the thoroughness of contact of the urea with the oil. Although the reaction is rapid at 450 F. and probably requires only a few minutes for completion, with only ordinary stirring of the urea with the oil several hours may be required.

In applying the process in a combined urea-clay treatment the ordinary clay-contacting processes known in the art may be employed. The type and amount of clay may be the same or approximately the same as in the ordinary type of operation when no urea is used. For example, an acid-treated clay may be used in amounts from 1 to 12 pounds per barrel of oil. The amount of urea may vary from 0.1 to 6 pounds per barrel oil with clay-treating conditions. The urea may be added to the oil in solid or molten form, before or during the clay contacting. Preferably a blanket of an inert gas, such as nitrogen, is used to prevent oxidation of the oil at the temperatures used, and agitation of the oilurea-clay mixture is carried out during the total contact time which may vary from 20 minutes to 1 hour. A 30-minute contact time at 450 F. with an acid-treated clay such as Filtrol 60 gives very satisfactory results as indicated by Example 5. Examples of adsorbents that may be used are Riverside fullers earth, natural Utah clay, alumina, bauxite, ball clay, china clay, montmorillonite and kieselguhr. The process may be applied during the distillation of lubricating oils. In the preparation of neutrals and bright stocks, particularly by vacuum distillation, most or all of the naphthenic acids and other oxygenated bodies can be converted into amides and related products, such as nitriles by mechanically proportioning urea into the oil during or before distillation. The solid or liquid urea may be added directly to the oil stream before it enters the fraction-ating tower. Urea may, if

desired, be added to the oil stream before it enters the furnace, or it may be added prior to entering the fractionating tower. The urea may be added in increments, one portion before the heater and another before the fractionating tower. Since under distillation conditions, some of the urea will undergo decomposition before amide or nitrile formation, the maximum effect is obtained by using an excess of urea over the stoichiometric requirements of the acids or other oxygenated compounds present in the oil. In ordinary operation of the process as a distillation, one and one-half to four times the stoichiometric amount of urea is used. The upper limit in the amount of urea used in the distillation technique is set by economic considerations. In actual commercial usage the amount of urea proportioned to the oil stream is determined by chemical analysis of the distillates and bottoms for neutralization number.

The distillation aspects of this invention are also applicable to the redistillation of oil such as a neutral, or bright stock, or a lubricating oil extract which contains an excessive amount of naphthenic acids or other oxygenated compounds. The operation applies to vacuum distillation with or without the use of steam or other inert gas. The process works best with the use of a minimum quantity of steam during the distillation.

The distillation, contacting and treating techniques and apparatus described in the following United States patents may be used in carrying out the instantprocess:

using the modifications herein described. Accordingly, the process of this invention comprises an improved method of reducing the neutralization number and/or odor of petroleum oils and related hydrocarbon mixtures by combined-urea-clay treatment, distillation in the presence of urea, or heating in the presence of urea, with or without the separation of the by-products herefrom, and under the conditions set forth. Although the invention has been explained by means of examples, these are merely illustrative and the only limitations attaching thereto appear in the appended claim.

The embodiments of the invention, in which an exclusive property or privilege is claimed, are defined as follows:

The method of reducing the acid neutralization number of hydrocarbons of the group consisting of bright stocks and solvent extracts obtained in the solvent refining of mineral lubricating oils which consists in distilling said hydrocarbons in the presence of urea at a temperature of about 400 to 550 F., and recovering distillates and residues having reduced acid neutralization numbers.

References Cited in the file of this patent UNITED STATES PATENTS 2,221,301 Kipper Nov. 12, 1940 2,253,638 McKennon Aug. 26,1941 2,341,329 Meyers Feb. 8, 1944 2,560,193 Shoemaker July 10, 1951 2,686,755 Hess et a1 Aug. 17, 1954 2,689,845 Dinersteen Sept. 21, 1954 2,746,948 Fetterly May 22, 1956 

